In a screen printer as described in commonly owned prior U.S. Pat. Nos. 3,974,766 and 3,998,156, for example, it is important that the longitudinal edges of the web remain straight and parallel as it passes the several printing stages. Even if there is no lateral deviation from the prescribed path, however, developing differences in longitudinal stress throughout the width of a broad textile web may give rise to internal deformations which tend to cause irregularities in an imprinted pattern. Thus, the more highly stressed warp threads of the fabric will generally more strongly contract, on account of their inherent elasticity, after the printing operation when the web is freed from the tension imparted to it by the feed rollers serving to advance it through the processing equipment, whereby the transverse lines of the pattern are distorted.